From WO2007072285 it is known to control lighting in a room dependent on the position of furniture. Dependence on furniture position may be a factor in a lighting system that controls the spatial distribution of light intensity and spectral properties in the room, which will be called a “light ambience”. A selected light ambience may be realized by means of a plurality of light sources at different points in the room and with selectable intensity and spectral content. Selection of a desired light ambience may be performed for example based on activities of users, such as watching television, conversation, reading etc. When a user watches a display screen for example, different light ambience selections may be made dependent on a classification of the content of the displayed information (romantic film, action film, video game etc.) or different light ambiences may be created based on the presented video frames using video content analysis or using light scripts dedicated to the content. Also, a user may manually control the ambience selection, usually by selection from preset options.
As a light ambience may involve many individual lighting parameters it is desirable that these parameters can be largely adjusted automatically, without requiring a user to set all parameters each time. However, such an automatic selection presents a challenge because it depends on the position of furniture in the room as well as the user's position and direction of attention. Furniture and persons can block light or affect the spectral distribution of reflected light. Moreover, different lighting parameters may be needed dependent on the user's position and direction of attention. For example lighting parameters may need to be controlled differently dependent on whether the corresponding light source is in front of the user, behind the user or on a side of the user.
To account for the effects of furniture and persons in the room WO2007072285 provides for the use of RFID tags attached to the furniture and the person's clothing. In this way the positions and identities of various objects can be determined by means of triangulation of RFID responses and the results can be used to adapt the control of the light sources. WO2007072285 also describes that instead of RFID tags other sensors may be used that are capable of receiving signals and transmitting information, such as infrared or ultrasonic transducers. However, to account for all lighting effects, this solution requires the overhead of providing all furniture and persons with transponders. As an alternative one may consider measuring the position of objects and persons by means of image processing techniques. Stereoscopy, or more abstractly identification of multiple light rays that impinge on objects and persons in the room, can be used to measure positions. However, such measurements require a calibrated setup, which may be impracticable in non-professional environments, like a home.